The disclosure relates to processing of audio signals that may include noise and echo and relates to devices that perform this processing.
Echo and noise control are desirable features on modern consumer electronic devices. For example, a number of consumer electronic devices are adapted to receive speech from a near end talker via microphone ports on a first device and transmit a signal representing this speech to a far end device (a second device) and concurrently output audio signals (such as speech from a user of the second device) that are received from the second device. While a typical example is a portable telecommunications device such as a mobile telephone, with the advent of voice over IP, desktop computers, laptop computers and tablet computers may also be used to perform voice communications. Moreover audio systems at home and in the car can also perform voice communications and may use echo and noise control.
In these full duplex communication devices, where both parties can communicate to the other simultaneously, the downlink signal that is output from the loudspeaker may be captured by one or more microphones and get fed back to the far end device as echo. This is due to the natural coupling between the one or more microphones and the loudspeaker; for example the coupling is inherent due to the proximity of the microphones to the one or more loudspeakers on a device. This echo can occur concurrently with desired near end speech and can often render the user's speech difficult to understand. Moreover, the echo of the far end talker can degrade the quality of the communication for the far end talker by distracting the far end talker when the far end talker hears her own voice.
At the same time noise (external to the device and user of the device) in the environment can also degrade the quality of communication. This generally affects all microphones and is independent of (and thus happens concurrently with) echo impairments.
Multiple microphones can be used to help control both echo and noise on a device. While there are techniques that can exploit multiple microphones to do noise control, and there are techniques to exploit multiple microphones to do echo control, how to simultaneously exploit microphones simultaneously for both uses can be tricky. One reason for this is that the impairments due to noise and the impairments due to echo can be different. For example, echo returned to a far-end user is a strong impairment. Here a far-end user can hear his/her own voice which can be very distracting. In extreme cases, this sometimes renders it impossible to talk. Echo returned to the far-end user of course also makes it difficult to understand the near-end user, assuming both users are talking at the same time. In contrast, noise sent to a far-end user mainly impairs the far-end user's ability to understand the near-end user. It does not necessarily distract the far-end user to the point of not being able to talk.